1. Field of the Invention
The present invention relates to a rotation table mounted onto a tool machine.
2. Description of the Related Art
A rotation table of a tool machine includes a clamping device or a braking device used to maintain an indexing angle during an indexing operation. When a piston inside the clamping device is pressed against a brake disk fixed to a rotation axis, the brake disk is clamped or held to be locked, so that the angle of the rotation axis is maintained. As an example of the rotation table of the tool machine, a table is known in JP-A 2009-248242.
FIG. 5 is a specific cross-sectional view illustrating a basic structure of a rotation table. An axis 2a of the rotation table is rotatably supported inside a casing 1 through a main bearing 3a and a support bearing 3b. 
A stator 4b of a motor and a cylinder 7b of a brake, a sensor head 5b, and a lid 8 are fixed to a casing, and a rotor 4a of the motor, a sensor gear 5a, and a disk 6 are fixed to the axis 2a so as to be rotatable along with the rotation table.
A piston 7a is formed so as to be movable forward and backward inside the cylinder 7b through seal members 7c to 7e, and is biased by a plurality of coil springs 7h in a direction in which the piston 7a moves toward the clamping device. Also, a forward movement air chamber 7f and a backward movement air chamber 7g are formed between the piston 7a and the cylinder 7b so that the piston 7a is movable by compressed air.
In an unclamped state, that is, a state where the clamping is released, compressed air is fed to the backward movement air chamber 7g by a switching valve such as an electromagnetic valve not illustrated in FIG. 5, and hence the piston 7a is movable to the backward movement end against the compressing force of the coil spring 7h. 
In a clamped state, air is discharged from the backward movement air chamber 7g and compressed air is fed to the forward movement air chamber 7f by the electromagnetic valve so that the piston 7a moves forward and the disk 6 is nipped between the piston 7a and a friction surface 8a on the lid 8.
In order to apply a force necessary for clamping the rotation axis, an air pressure or an oil pressure using a pressure fluid is used, and the switching valve is used to switch the clamped state and the unclamped state. In many cases, the switching valve is provided inside the rotation table since the responsiveness of the piston becomes better as the switching valve becomes closer to the clamping device.
In many cases, the switching valve used to switch the clamping operation and the unclamping operation is provided inside the rotation table so as to be located inside the casing 1 as illustrated in FIG. 6 in order to improve the responsiveness of the piston 7a. In general, a flow passageway used to connect a switching valve 9 and a clamping device 10 to each other is formed by a joint 13 and a pipe 14.
In this case, since there is a need to dispose the joint 13 and the pipe 14 between the clamping device 10 and the switching valve 9, there is a need to attach or detach the pipe 14 connecting the clamping device 10 and the switching valve 9 to each other during the maintenance thereof, and hence a problem arises in that the maintenance requires a time. Further, there is a need to ensure a space for attaching or detaching the pipe in accordance with the arrangement of the clamping device 10 and the switching valve 9, and hence a decrease in the size of the rotation table may be disturbed.